The Department of Homeland Security (DHS) is concerned about the rate at which outlawed signal-jamming devices are being found across the US.

In a warning issued on Wednesday, it said it has seen an 830 percent increase in seizures of these signal jammers since 2021, specifically those made in China.

Signal-jamming devices are outlawed in the US, mainly because they can interfere with communications between emergency services and law enforcement.

While the Communications Act of 1934 effectively prohibits such devices, signal jammers of the type DHS is concerned about have only circulated in the last 20 to 30 years.

Authorities have paid special attention to relay attack devices in recent years – the types of hardware that can be used to clone signals used by systems such as remote car keys, although the first examples of these devices date back to the 1980s.

Likewise, Wi-Fi and cell phone jammers have only become useful in the 21st century despite the underlying radio tech already existing in some form decades earlier.

GPS jammers also fall under this category, and in recent years have been said to present "significant challenges" to air travel safety.

A recent spate of jamming activity around airports in Cyprus led to a fifth of flights being affected, according to EU airspace regulator Eurocontrol.

Focusing on the Chinese-made jammers, the DHS said the companies behind their manufacture have "attempted to subvert inspection," increasing the threat to critical infrastructure.

Specific examples it provided included unauthorized immigrants jamming calls to police departments to stymie responses to home invasions and bank robberies. It said cases of this have been seen in Florida, Illinois, Ohio, Pennsylvania, Texas, Vermont, and Virginia.

It also said officers recovered one such jamming device in Texas in February while arresting an illegal immigrant from Chile, and in December, one was used to hamper police response to a domestic burglary.

A DHS spokesperson said: "Signal jammers have been used by illegal aliens across the country to jam communications during police operations, bank robberies, burglaries, and other dangerous crimes.

"Under the vigilance of [Customs and Border Protection], national security begins at America's ports. As Chinese manufacturers attempt to smuggle signal jammers, we will continue to seize these tools of terrorism. President Trump and Secretary Noem will always protect America's critical infrastructure and law enforcement."

As in the US, signal jammers are also illegal in the UK, which paid special attention to them in February as lawmakers introduced new rules against vehicle key and key fob jammers as part of the Crime and Policing Bill.

The most recent figures from the Crime Survey for England and Wales showed there were 744,000 vehicle thefts in 2023 alone, and signal-jamming and signal-manipulating devices were used in around 36 percent of these thefts.

Both in the US and UK, once the Crime and Policing Bill is passed, it will be illegal to import, operate, manufacture, adapt, or sell any signal-jamming devices that could be used to interfere with emergency services communications or critical infrastructure.

Regarding a desired crackdown on their distribution, Homeland Security said it thinks China "could be amenable to cooperation" on the topic of signal jammers since public use is also banned in Beijing. ®